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Genes and polypeptides
1)
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2)
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3)
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The base sequence of a gene determines the amino acid sequence in a
polypeptide
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The triplet code is degenerate (i
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one amino acid is coded for by more than one
triplet
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Helicase unwinds DNA
RNA polymerase synthesises RNA (using complementary base pairing to
incorporate the correct nucleotide by condensation reaction
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Transcription: DNA rewritten as RNA
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Like DNA, mRNA is a nucleic acid, but…
i)
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It contains ribose instead of deoxyribose
iii)
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8)
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(I
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each base is only part of one triplet /
codon, and each triplet codes just one amino acid)

The structure of the heart
1)
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The aorta is connected to the left ventricle and carries oxygenated blood to all
parts of the body except the lungs
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The pulmonary artery is connected to the right ventricle and carries deoxygenated
blood to the lungs, where its carbon dioxide is removed
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4)
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They branch off the aorta
shortly after it leaves the heart
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5)
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*Atrioventricular valves close when the pressure is higher in the ventricle than the
atrium due to ventricle contracting
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*Semi-lunar valves close when the pressure in the artery is greater than in the
ventricle, due to ventricle relaxing

The cardiac cycle
1)
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2)
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3)
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Cardiac output=heart rate x stroke volume

Coronary heart disease
1)
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Atheroma increases the risks of thrombosis and aneurysm
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Low density lipoproteins: Saturated animal fat
High density lipoproteins: Unsaturated fats (e
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Vegetable oils)
HDLs help to remove LDLs
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Risk factors (Factors linked to an increased risk in CHD):
*Too much saturated fat
*Gender
*Ethnicity
*Lack of exercise
*Age
*Smoking
*High blood pressure (more likely to develop aneurysm and burst, causing
haemorrhage; artery walls become thickened and hardened therefore restrict
blood flow)
*Blood cholesterol
*Diet (High levels of salt raise blood pressure; high levels of saturated fat increase
LDL levels and blood cholesterol concentration)
4)
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Myocardial infarction:
*Atheroma raptures
*Formation of blood clot (thrombus)
*No blood flow to cardiac muscle
*No oxygen supply to cardiac muscle
*Cardiac muscle dies
*Myocardial infarction

Gas exchange in a leaf of a plant
1
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*Diffusion takes place in the gas phase (more rapid than in water)
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2
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3
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*Stomata are completely or partly closed when water loss would be excessive in
order to balance the conflicting needs of gas exchange and control of water loss

Gas exchange in fish
1
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They have developed a specialised
internal gas exchange surface: the gills
...
Gills:
*Made up of gill filaments
*Gill lamellae are at right angles to gill filaments
*Gill lamellae increase the surface area for gas exchange
*Water is taken in through the mouth and forced through the gills
3
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This is known as a countercurrent flow
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The countercurrent ensures maximum gas exchange
5
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*Blood that’s already oxygenated meets the water which has its maximum oxygen
concentration
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*Deoxygenated blood meets water which has had most of its oxygen removed
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*Therefore there is a fairly constant rate of diffusion across the entire gill plate
...
The countercurrent system maintains a difference in oxygen concentration and a
diffusion gradient across the whole length of the gill lamellae
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Single-celled organisms are small – Large surface area to volume ratio
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Insects:
Efficient gas exchange requires a thin, permeable surface with a large area, this
leads to water loss (dehydration)
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Tracheae and tracheoles:
Oxygen concentration towards the ends of the tracheoles falls
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Ventilation: movement of muscles create mass movement of air in and out of
tracheae
4)
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Insects rely on diffusion to exchange gas between the environment and the cells
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Factors affecting transpiration and potometer
1)
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As a side effect that also increases transpiration
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2)
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3)
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4)
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5)
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*Therefore long periods of light, heat or dry air could result in decrease in
transpiration when the stomata close
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Accuracy of a photometer:
*A photometer actually measures the rate of water uptake by the cut stem, not
the rate of transpiration
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*During the day plants often transpire more water than the take up and during the
night plants may take up more water than they transpire
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Circulatory system in mammals
1)
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*Exchange:
-- Supply metabolic materials (Oxygen; Glucose; Mineral ions; Amino acids)
--Remove waste products (Urea; Heat and Carbon dioxide)
2)
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There is relatively high hydrostatic pressure at the arteriole end of the capillary and
relatively low hydrostatic pressure at the venous end of the capillary
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Reasons for falling pressure:
*Liquid leaves blood vessel to form tissue fluid
*Friction / Resistance
5)
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If the
osmotic pressure is higher than the hydrostatic pressure, water moves into capillary;
if the osmotic pressure is smaller than the hydrostatic pressure, water moves into
lymphatic vessel
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*The loss of tissue fluid from the capillaries reduces the hydrostatic pressure inside
them
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*Osmotic forces resulting from the proteins in the blood plasma pull water back into
the capillaries
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The lymphatic system:
*The primary function of the lymphatic system is to carry excess tissue fluid back to
the blood
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*Valves are present to prevent backflow
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The tissue fluid:
*Tissue fluid is formed from the blood plasma
*Tissue fluid contains glucose; amino acids; fatty acids; slats and oxygen
*Tissue fluid receives carbon dioxide and other waste material from tissues
4)
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*So at the arterial end of the capillaries, this hydrostatic pressure forces water and
small molecules through the endothelium out of the blood plasma
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*However, the hydrostatic pressure of the tissue fluid prevents outward movement
of liquid from capillaries
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5)
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g
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*Capillaries contain only the endothelium, so there is a short diffusion distance,
allowing rapid diffusion of materials between the blood and the cells
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